Thin film resistors are utilized in electronic circuits in many diverse technological applications. The resistors may be part of an individual device, or may be part of a complex hybrid circuit or integrated circuit. Some specific examples of thin film resistors in integrated circuits are the resistive ladder network in an analog to-digital converter, and current limiting and load resistors in emitter follower amplifiers.
Film resistors can comprise a variety of materials including polysilicon, tantalum nitride (TaN), silicon chromium (SiCr), and nickel chromium (NiCr), as well as other metals. These resistor materials are generally evaporated, sputtered, or CVD deposited onto a substrate wafer at a metal interconnect level and subsequently patterned and etched. The thin film resistors require an electrical connection to be made to them. Thus, two mask layers are required typically for fabrication: one to form the resistor film itself and the other to form the resistor “heads” or contact points of the resistor. Connection is then made typically from an overlying metal interconnect layer to the resistor heads.
High precision analog circuits rely heavily on the performance of passive circuit components such as resistors and capacitors. Consequently, it is advantageous to provide an accurate description of such components for their simulation in circuit simulation tools such as SPICE.